Along with the recent development of small-sized and thinner-type electronic machinery and tools (electronic devices), there has been strong demand for the establishment of higher-density packaging technique of semiconductor elements. The method using a lead frame, which method has been used for packaging a semiconductor device so far, fails to cope with the demand for such high-density packaging. Also, a method of primarily using a resin paste, among die bonding materials used for bonding these, is currently dominant.
For this, flip-chip packaging is proposed as a method to package a semiconductor device having the substantially same size as a semiconductor element. This flip-chip packaging has attracted remarkable attention as a method of packaging semiconductor elements in a minimum area, corresponding to the current development of small-sized and high-density electronic machinery and tools. A bump is formed on an aluminum electrode of a semiconductor element used for this flip-chip packaging, and the bump is bonded with wiring on a circuit substrate electrically. As to the composition of the bump, a solder is primarily used, and this solder bump is formed on an aluminum terminal that is exposed and connected to the internal wiring of a chip by deposition or plating. Other examples of the bump include a gold stud bump formed in a wire bonding device.
If a semiconductor device connected by such a flip-chip is used as it is, the electrode of the connected portion is exposed to the air, and large stress is applied to the connected portion of the bump through thermal history in the subsequent step of, for example, a solder reflow step, because of a large difference in the thermal expansion coefficient between a chip and a substrate, giving rise to a problem concerning packaging reliability.
To solve this problem, a method is adopted in which, after the bump is connected with the substrate, the gap between the semiconductor element and the substrate is filled with a resin paste or an adhesive film, which is then cured to fix and secure the semiconductor element to the substrate, to improve reliability of the connected portion.
Also, a tape is proposed as a removable adhesive or adhesion tape to be used from a dicing step to a die bonding step. However, it has been found that a removable adhesive or adhesion agent used for bonding after UV curing for this purpose has difficulty in retaining resin fluidity, due to the formation of a three-dimensional crosslinking structure associated with UV radiation. Therefore, the filler cannot satisfactorily be filled into the substrate irregular surface, rendering it impossible to obtain bonding reliability.
In the meantime, generally, semiconductor elements subjected to flip-chip packaging have many electrodes, and also these electrodes are arranged around the semiconductor element because of a circuit design problem. Therefore, if a liquid resin is poured from the gap between electrodes of these semiconductor elements by a capillary phenomenon when a resin paste is filled, the resin spreads insufficiently, which readily allows the presence of unfilled portions, posing problems, including such operational inferiority as that the action of the semiconductor element tends to be unstable, and low-reliability moisture resistance. Further, when the size of a chip is smaller, the substrate is contaminated by an overflowed liquid resin, and when the electrode pitch is narrowed, it makes for difficulty in pouring the resin. Also, it takes too much period of time to fill the resin in each flip-chip-connected semiconductor element, which can represent a productivity problem, considering the curing step. A method in which a wafer is diced into chips after an adhesive film is bonded by thermocompression at one time, is more simplified in steps than the method of filling a resin paste, and is hence advantageous. However, because a wafer is damaged more easily at the time of thermocompression bonding, as the thickness of the wafer is decreased, which increases the need to grind or cut the backing face of the thick wafer after the adhesive film is bonded by thermocompression.
However, in a conventional combination of back face grinding removable adhesive tape and an adhesive film, this tape has high affinity to the adhesive film, giving rise to the problem that peeling force after the backing face is ground tends to be increased, and therefore damage to the wafer is easily caused in a peeling step. Also, to improve the fill-ability of the adhesive film into irregular substrate, to thereby increase bonding reliability, it is necessary to lower melt viscosity when the adhesive film is applied under heating. However, the peeling force of the adhesive film from the removable adhesive tape tends to be increased by application and adhesion under heating, posing the problem that it is difficult to peel the adhesive film from the removable adhesive tape after adhesion under heating.
Other and further features and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawings.